Method of and apparatus for dispensing gases



April 10, 1956 P. M. SCHUFTAN METHOD OF AND APPARATUS FOR DISPENSINGGASES Filed Aug. 26, 1952 .hoEEzmcou cmwnxo msowmmw INVENTOR PAUL M.SCHUFTAN BY 'A ORNEY United States Patent METHGD OF AND APPARATUS FORDESPENSHIG GASES Paul Maurice Schuftan, Richmond Hill, England, assignorto The British Oxygen Company, Limited, a British company ApplicationAugust 26, 1952, Serial No. 396,4ll8

Claims priority, application Great Britain August 27, 1951 17 Claims.c1. 62-1) The present invention relates to the dispensing of gases, theboiling points of which are below or not substantially above atmospherictemperature, and more particularly to a method whereby a fluctuatingdemand for such a gas may be met from a continuous and relatively steadysupply of such gas.

Such conditions are met with, for example, in air separation plantsdesigned primarily for the production of liquid oxygen but adapted tosupply a fraction of the oxygen output as gas for pipe linedistribution. A fluctuating demand for oxygen is similarly experiencedwith small separation plants operating directly to supply oxygen forimmediate use, for example, in steel manufacture and for oxygen cuttingand welding.

in al such cases, attempts to design separation plant of suifcientflexibility to cope with the varying demand have involved seriousdifiiculties and involve a considerable increase in the capital cost ofthe plant.

it is an object of the present invention to provide a method ofdispensing a gas of the type specified so as to meet a fluctuatingdemand from a continuous supply of gas at a steady rate, such thatsufdcient gas is always available to satisfy periods of high demand andno loss of gas occurs during periods of low demand.

According to the present invention, such a method for dispensing a gasof the type specified comprises supplying excess gas, available duringperiods when the supply of gas exceeds the demand, at a pressure inexcess of the demand pressure to a storage medium comprising a mass ofthe liquefied gas, and evaporating gas from the storage medium underreduced pressure during periods when the demand exceeds the supply ofgas.

For the sake of clarity, the invention will be described in more detailas applied to the dispensing of gas from an air separation plant inwhich there is fluctuating demand for gaseous oxygen, but it is notlimited to installations of this type. it may, for example, be appliedto air separation plants in which the demand is for nitrogen or toplants for the separation of gas mixtures other than air, such as, forexample, coke oven gas, or to any other system in which a fluctuatingdemand for gas has to be met from a steady supply.

When the excess product to be stored is gaseous oxygen, the storagemeans will comprise a suitable vessel insulated to reduce cold losses,and partially filled with liquid oxygen, the quantity of liquidnecessary and hence the size of the vessel being governed by the extentof the fluctuations in demand which are to be anticipated.

The vessel is provided with suitable means, such as a series of chargingnozzles immersed in the liquid, by which ox gen at the storage pressureand at condensation temperature may be supplied to the body of theliquid and is also provided with means by which gaseous oxygenevaporating from the surface of the liquid inthe vessel may pass to themain delivery line.

in operation, when the demand for oxygen is less than the availableoutput of the plant, the excess oxygen after compression to the storagepressure will pass to the storage liquid and will be condensed therein.The pressure within the storage vessel will tend to rise until thestorage pressure is reached. Should, however, the demand exceed thesupply of oxygen, the pressure Within the storage vessel will fall andoxygen will evaporate from the liquid and pass to the delivery line. Itwill be apparent that a suitable valve system must be provided to ensureauto-- matic operation of the storage system.

Excess oxygen leaving the separation plant will be in a superheatedstate and after compression to the required pressure it must be cooledto saturation temperature before contacting the storage liquid. This mayconveniently be effected by passage of the oxygen through a regenerator,the regenerator being subsequently recooled by passage through it ofoxygen evaporated from the storage medium during a period of increaseddemand.

Where the oxygen leaves the separation plant in the form of gas, it maybe compressed to the storage pressure by any suitable form ofcompressor. However, in many cases, the oxygen will leave the plant asliquid and in this case the liquid oxygen may be brought to the storagepressure by a suitable liquid pump and subsequently vaporized by anysuitable means, such as, for example, by heat exchange with the air feedto the plant, prior to contacting the storage liquid.

Since the storage liquid will be at a temperature considerably belowatmospheric temperature, the provision of adequate insulation for thestorage vessel to minimize cold losses is essential. For this purposevacuum insulation been found to be particularly suitable. Some coldlosses from the storage vessel are, however, bound to occur and in caseswhere the oxygen leaves the gas plant in the form of a liquid and isforced to the storage pressure by a liquid pump, such cold losses may becompensated by directing a part of the liquid oxygen from the liquidpump direct to the storage vessel, provision being made to preventoverfilling of the storage vessel during prolonged periods of lowdemand. Alternatively, cold losses may be compensated by cooling thestorage liquid from external sources by either direct or indirect heattransfer.

The initial supply of liquid oxygen to the storage vessel mayconveniently be derived from the initial operation of the gas separationplant. Moreover, the liquid oxygen contained in the storage vessel formsa convenient source of oxygen and cold for use in the rapid recooling ofthe separation plant after thawing. This will further aid in ensuringcontinuity in the supply of oxygen.

This invention will now be more particularly described with reference tothe accompanying drawing which shows diagrammatically an exemplaryapparatus for carrying out a method of dispensing gaseous oxygen to meeta fluctuating demand from a supply provided by a conventionaldouble-column air-separation plant producing liquid oxygen.

Air, after treatment in a carbon-dioxide-removing device lll, is fedthrough pipe 11 to compressor 12 where it is compressed. The compressedair leaving the compressor 12 is treated in a moisture-removing device13, and

upon leaving the device 13 through pipe 13' divides, part of it passingthrough a passage 14 in a main heat exchanger H where it is cooled byindirect heat exchange with the separation products and thence via pipe15 through an expansion valve 16 to the lower column 17 of aconventional double column A; The remainder of the air passes throughpipe 19 to an expansion engine 2!) where it is expanded to the lowercolumn pressure and thence through pipe 21 to rejoin the other part ofthe air entering the lower column.

In the lower column 17, there accumulates at the base an oxygen-richfraction which is transferred through pipe 22 and expansion valve 23 tothe upper column .24 of the Patented Apr. 10, 1956 a vacuum insulationtype.

column 17 there accumulates at is a nitrogen-rich fraction which istransferred through pipe and expansion valve 2-6 to the top of the uppercolumn 24.

in the upper column the air is'separated into: a nitrogen fraction whichleaves the top or" the column through pipe; 27 and passes to the heatexchanger H and thence to waste, and a liquid oxygen f action whichcollects at the base of the upper column.

This liquid oxygen fraction is withdrawn throng 2.8, from which a partof the fraction as the average demand for gaseous oxygen is withdrawnthrough pipe 29 while the remainder passes through a branch pipe 31 andvalve 31 therein to storage and use as liquid.

The dispensing means preferably comprises a twostage liquid pump, thefirst stage 32 of which is fed with liquid from pipe 29 and is adaptedto elevate the pressure of the liquid to the demand pressure. From theoutlet of this stage a pipe leads to a passage 33 through the heatexchanger H and from thence through conduit 34 to the installation usingthe oxygen.

The second stage 35 of the liquid pump is adapted to further elevate thepressure of the liquid oxygen to the storage pressure which must behigher than the demand pressure.

the warm end of which a conduit 38 connects passage 37 to the conduit 34which conducts gas to the oxygenusing installation. From pipe 38, abranch pipe 39 leads to the upper end of a regenerator 40 of suitableconstruction, such as a chamber filled With a heat-storage material,from the lower end of which a pipe 41 leads through a non-return valve42 to a series of discharge nozzles 43 immersed within a storage mass440i liquid oxygen partially filling a vessel 45. To prevent loss ofcold from the liquid oxygen storage mass, the vessel 45 is provided withadequate insulation, preferably of the The regenerator 40 is alsoinsulated. The lower end of regenerator do is also connected by pipe 46with the gas space above the liquid 44 in vessel 45. A nonreturn valve47 is also preferably interposed in pipe 46. The storage mass is adaptedto be isolated from either the liquid pump 35 or the pipe 34 leading tothe user installation by means of valves 43 and 49, respectively,interposed in pipe 38 on either side of the junction with pipe 39.

Valves 48 and 49 are openable respectively in response to thebelow-normal or above-normal demand for oxygen. For example, valve 48may be constructed to be openable automatically in response to a smallpressure increase in conduit 34 caused by the reduction in demand by theconsumer and valve 49 may be constructed to be openable automatically inresponse to a small pressure decrease in conduit 34 caused byabovenorrnal demand;

In spite of the insulation of vessel 45 some cold losses are bound tooccur, and to replace these a branch pipe line 59 controlled by valve 51is connected directly between pipe 36 and vessel 45, by-passing heatexchanger H, through which liquid oxygen at the storage pressure may beadded directly to the'storage mass 44. A connection 52 controlled by astop valve 53 may be provided with pipe to permit addition of liquidoxygen to the vessel 45 from an external source such as a liquidoxygentransport device, or for use in withdrawing liquid oxygen from thestorage mass 44 when desired, for example, if some of the stored liquidis to be used for rapid cooling of the column A after an interruption ofoperation. Suitable liquid-level gauges and safety devices may also beprovided; for example, a safety excess-pressure relief valve 54 may beconnected to conduit '38 between the valves 48 and '49. 4

In operation, when the demand for gaseous oxygen equals the output ofliquid oxygen from the plant other From the outlet of this stage a pipe36 connects to a passage 37 through'heat, exchanger H from than thatwithdrawn as liquid at connection 31, the liquid oxygen, after elevationto the demand pressure in the first stage 32 of the pump, is passedthrough pipe 39 to heat exchanger passage 33 wherein it is vaporized byindirect heat exchange with the incoming air, and thence through pipe 34to the user installation.

In these circumstances, both valves 43 and 49 remain closed.

Should the demand for oxygen fall, not all the liquid 0 gen pumped bythe first stage 32 of the pump will be to satisr'y the demand. Theexcess liquid is passed to the second stage 35 of the pump and istherein elevated to the storage pressure. Thence it is passed throughpipe 36 to the heat exchanger passage 37 where it is vaporized by heatexchange with the incoming air, and the resulting gas passes throughvalve 48, which opens automatically, to pipe 32 since valve 49 remainsclosed. The gas which is in a superheated state is cooled by passagethrough the heat-storage filling of regenerator 40, which has itselfbeen cooled by passage therethrough of vapors evolved from the storagemass 44' in a previous cycle as hereinafter described. From theregenerator, the gas passes through pipe 41, check valve 42, and isdischarged through the nozzles 43 into the storage liquid 44, by whichit is absorbed. This absorption will cause the pressure within thevessel 44 to rise'until the storage pressure is reached.

If the demand for gas exceeds the supply from the plant, valve 49 willbe opened automatically while valve 48 will remain closed. Under theseconditions, the pressure within vessel 45 will fall and oxygen willevaporate from the storage mass 44. This vapor is withdrawn through pipe46 and check valve 47 and passes through regenerator 4%, which it cools,and thence passes through 0 pipe 39, valve 49, and pipe 34 to the userinstallation.

to cover all changes and modifications of the process and V apparatusdisclosed which fall within the spirit and scope of the invention. Forexample, the gas separation plant A may be of the type that produces theproduct gas as gas at a low pressure, and in place of pumping the liquidproduct to the desired pressures before heating it, the gaseous productafter heating may be compressed to the desired pressures for storage orfor delivery to the consumer.

I claim:

1. In a method of dispensing a gas having a boiling point below about 21C. to a consumer having a fluctuating demand at a demand pressure from asupply source providing the gas at a continuous and relatively steadyrate the improvement which comprises providing a confined storage bodyof the gas in liquid state; passing the excess gas, available from thesupply when the rate of supply exceeds the demand, at a pressure higherthan the demand pressure into direct and intimate contact with thestorage body liquid; providing for increasing vapor pressure acting onthe storage body to effect condensation in and combination with thestorage body of said excess gas, the temperature of the stored liquidbeing correspondingly increased; and, during periods when the demandexceeds the supply rate, supplying the excess demand by passing gas fromsaid storage body to said consumer at reducing vapor pressure forevaporating stored liquid and correspondingly reducing the temperaturethereof.

2. In a method of dispensing a gas according to claim 1, the step ofmaintaining a liquid level between liquid and vapor phases of saidstorage body above a predetermined minimum by adding portions ofliquefied gas to said storage body as and when required to compensatefor losses therefrom tending to reduce the liquid level thereof belowsaid desired minimum.

3. In a method of dispensing a gas having a boiling point below about 21C. to a consumerhaving a fluctuating demand at a demand pressure from asupply source providing the gas at a continuous and relatively steadyrate the improvement which comprises providing a confined storage bodyof the gas in liquid state; passing the excess gas, available from thesupply when the rate of supply exceeds the demand, at a pressure higherthan the demand pressure into heat exchange relation with a cooled heatstorage mass for cooling said excess gas; passing the cooled excess gasinto direct and intimate contact with the storage body liquid; providingcondensation in and combination with the storage body liquid of saidexcess gas at increasing vapor pressure and corresponding increasingtemperature of the liquid; and during periods when the demand exceedsthe supply rate, supplying the excess demand by passing gas from saidstorage body in heat exchange relation with said heat storage mass tosaid consumer for cooling the mass and heating the gas; and effectingsuch passage at reducing vapor pressure for evaporating stored liquidand correspondingly reducing the temperature thereof.

4. In a method of dispensing a gas according to claim 3, the step ofmaintaining a liquid level between liquid and vapor phases of saidstorage body above a predetermined minimum by adding portions ofliquefied gas to said storage body as and when required to compensatefor losses therefrom tending to reduce the liquid level thereof belowsaid desired minimum.

5. In a method of dispensing a gas having a boiling point below about 21C. to a consumer having a fluctuating demand at a demand pressure from agas mixture separating plant that separates the gas mixture by lowtemperature rectification and produces the gas at a production ratecontinuously for long operating periods for delivery from the plant at apressure at least equal to the demand pressure the improvement whichcomprises providing a confined storage body of the gas in liquid state;passing excess gas produced by the plant when the production rateexceeds the demand into heat exchange relation with a cooled heatstorage mass for cooling said excess gas; passing the cooled excess gasinto direct and intimate contact with the storage body liquid; providingcondensation in and combination with the storage body liquid of saidexcess gas at increasing vapor pressure and corresponding increasingtemperature of the liquid; and during periods when the demand exceedsthe production rate, supplying the excess demand by passing gas fromsaid storage body in heat exchange relation with said heat storage massto said consumer for cooling the mass and heating the gas; and effectingsuch passage at reducing vapor pressure for evaporating stored liquidand correspondingly reducing the temperature thereof.

6. In a method of dispensing a gas according to claim 5 in which the gasis produced in the liquid state at a low pressure, is pumped to thepressure at least equal to the demand pressure, and is vaporized andwarmed at such pressure.

7. In a method of dispensing a gas according to claim 5 in which the gasis produced in the liquid state at a low pressure, is pumped to thepressure at least equal to the demand pressure, and is vaporized andwarmed at such pressure; and in which the vaporization and warming iseifected by heat exchange with gas mixture to be separated.

8. In a method of dispensing a gas according to claim 5 in which the gasis produced in the liquid state at a low pressure, is pumped to thepressure at least equal to the demand pressure, and is vaporized andwarmed at such pressure, which includes adding portions of the prodnotin the liquid state to said storage body as required to compensatelosses therefrom tending to reduce the level of liquid of the storagebody below a desired minimum.

9. In a method of dispensing a gas according to claim 5 in which the gasis produced in the liquid state at a low pressure, and including thesteps of pumping the portion 6 of the product in liquid state thatcorresponds to the dc mand pressure; vaporizing and delivering saidportion to the consumer; and pumping the portion of the product inliquid state that corresponds to said excess gas to a pressure higherthan the demand pressure, and warming it before passage in heat exchangewith the heat storage mass.

10. In a method of dispensing a gas according to claim 5 which includesadding liquefied gas having a composition similar to that of the storagebody from an external source to said storage body as required tocompensate losses therefrom tending to reduce the level of liquid of thestorage body below a desired minimum.

11. Apparatus for dispensing a gas having a boiling point at atmosphericpressure below about 21 C. to consumer means having a fluctuating demandfrom a supply means delivering the gas at a continuous and relativelysteady rate, which apparatus comprises means for delivering the gas tosaid consuming means at a demand pressure; a storage medium comprisingan insulated pressure vessel holding a mass of the gas in the liquidstate and providing a vapor space above the liquid; means including aconduit opening below the level of the mass of liquid gas and operablewhen the demand by the consumer means is less than said rate for passingthe excess gas at substantially saturation temperature and at increasingpressures higher than said demand pressure into said vessel through saidmass of liquid gas so as to effect condensation of such excess gas; andmeans operable when the demand by the consumer means exceeds said ratefor withdrawing gas from said storage medium at reducing pressures andpassing it to said consuming means to augment the gas from the supplymeans.

12. An apparatus according to claim 11 in which said supply means is aplant for the low-temperature separation of a gas mixture producing saidgas at said continuous and relatively steady rate.

13. An apparatus according to claim 11 in which said storage medium alsoincludes a heat exchange device having heat storage material constructedand arranged for cooling the excess gas when it passes into the liquidmass and for being cooled by gas drawn from the liquid mass duringperiods when gas is supplied from the storage medium to the consumermeans.

14. An apparatus according to claim 11 which includes means for feedingliquefied gas to said storage medium as required to compensate lossestherefrom.

15. An apparatus according to claim 12 in which said plant produces thegas in a liquid state, and which includes liquid pumping means andvaporizing and superheating means operable to pump and heat the productto the demand pressure and temperature, and operable to pump the productto the storage pressure and heat it to the demand temperature when theproduct in excess of demand is to be passed to the storage medium.

16. An apparatus according to claim 12 in which said plant produces thegas in a liquid state, and which includes liquid pumping means andvaporizing and super heating means operable to pump and heat the productto the demand pressure and temperature, and operable to pump the productto the storage pressure and heat it to the demand temperature when theproduct in excess of demand is to be passed to the storage medium; andmeans for passing a portion of product from said pumping means in theliquid state directly to said storage medium.

17. Apparatus for dispensing a gas having a boiling point at atmosphericpressure below about 21 C. to consumer means having a fluctuating demandfrom a plant for the low-temperature separation of a gas mixtureproducing said gas as a product at a continuous and relatively steadyrate, which apparatus comprises means for delivering said product at ademand pressure to said consuming means; a storage system comprising aninsulated pressure vessel holding a body of the gas in the liquid state,a heat exchange device having heat storage material constructed andarranged .for cooling gas product by heataexchange 'with heat' storagematerial and cooling said heatestorage material by heat exchange withvapors of said body; valve-controlled means connected and operabletopass excess product, when demand by the consumer means is less than saidrate, at a pressure above the demand pressure through said heat exchangedevice into said body of liquid; and valve-controlled means connectedand operable to efiect vaporization from said body of liquid at reducingpressure, When demand by the consumer means exceeds said rate, andpassage of the resulting vapors through said heat exchange device tosaid product delivering means.

ieferences Cited in the file of this patent UNITED STATES vPATENTS

11. APPARATUS FOR DISPENSING A GAS HAVING A BOILING POINT AT ATMOSPHERICPRESSURE BELOW ABOUT 21* C. TO CONSUMMER MEANS HAVING A FLUCTUATINGDEMAND FROM A SUPPLY MEANS DELIVERING THE GAS AT A CONTINUOUS ANDRELATIVELY STEADY RATE, WHICH APPARATUS COMPRISES MEANS FOR DELIVERINGTHE GAS TO SAID CONSUMING MEANS AT A DEMAND PRESSURE; A STORAGE MEDIUMCOMPRISING AN INSULATED PRESSURE VESSEL HOLDING A MASS OF THE GAS IN THELIQUID STATE AND PROVIDING A VAPOR SPACE ABOVE THE LIQUID; MEANSINCLUDING A CONDUIT OPENING BELOW THE LEVEL OF THE MASS OF LIQUID GASAND OPERABLE WHEN THE DEMAND BY THE CONSUMMER MEANS IS LESS THAN SAIDRATE FOR PASSING THE EXCESS GAS AT SUBSTANTIALLY SATURATION TEMPERATUREAND AT INCREASING PRESSURES HIGHER THAN SAID DEMAND PRESSURE INTO SAIDVESSEL THROUGH SAID MASS OF LIQUID GAS SO AS TO EFFECT CONDENSATION OFSUCH EXCESS GAS; AND MEANS OPERABLE WHEN THE DEMAND BY THE CONSUMERMEANS EXCEEDS SAID RATE FOR WITHDRAWING GAS FROM SAID STORAGE MEDIUM ATREDUCING PRESSURES AND PASSING IT TO SAID CONSUMING MEANS TO AUGMENT THEGAS FROM THE SUPPLY MEANS.